The present invention is a sample delivery apparatus which can by used to repetitively deliver a sample to a process or an analyzer, either automatically or on demand. The sample delivery apparatus can be sealed under an inert atmosphere, thus minimizing the possibility of changes in the calibration standard due to, for example evaporation, hydrolysis, or oxidation. The design of the apparatus is such that only the volume of the actual sample delivered is consumed. Therefore, a large number of samples can be delivered with minimum consumption of sample material. The sample delivery apparatus can he used to deliver both liquid and gaseous fluids. The present apparatus is especially useful as an automated method for delivering a sample to calibrate on-line analyzers used to monitor chemical processes. A variety of indirect and direct methods exist for calibrating on-line analyzers In a typical indirect method, a sample is periodically collected from the process stream, analyzed in a separate analyzer, and the on-line analyzer adjusted to agree with the off-line analysis. This method is subject to errors resulting for example, from compositional differences in the sample analyzed in the online analyzer and the sample analyzed in the off-line analyzer, from compositional changes in the sample collected for off-line analysis due to handling, and from random variation in both the off-line and on-line analysis.
The direct method of calibration avoids many of the sources of error incurred in the indirect method of calibration by introducing a prepared standard directly into the analyzer. Typically, direct calibration is done by flushing and filling the analyzer's sampling system with a calibration standard delivered from a pressurized reservoir. However, this procedure is wasteful since only a minor portion of the standard is used for calibration with the majority of the standard being consumed in flushing the sample system. An alternative direct calibration method involves injecting the calibration standard into the analyzer through an auxiliary septum-type inlet system by means of a syringe. Although syringe injection is less wasteful, it risks exposure of the calibration standard to the atmosphere, which can cause changes in composition when reactive materials are involved.
The biggest problem with the described calibration procedures is that they are manual in nature. As a result, they are time consuming and potentially hazardous. Consequently, the calibration of on-line analyzers have tended to be done infrequently and even when conducted the results are often inaccurate.
Therefore, an objective of the present invention is to provide an apparatus which can automatically and repetitively provide a sample of a material to an analyzer or a process. Another objective is to provide an apparatus which can be maintained under substantially inert conditions during multiple deliveries of a sample. Finally, it is an objective of the present invention to provide an apparatus which minimizes the total amount of sample required and essentially eliminates the loss of sample due to flushing of the cell used to deliver the sample.